The present invention relates to a method for manufacturing a golf club head, more particularly to a structure of the sole portion capable of lowering the center of gravity of the head.
In recent years, wood-type club heads for drivers and the like are increased in the volume, while preventing the weight from increasing. As a result, it becomes very difficult to set the center of gravity of the head at the desired position because there is almost no weight margin which can be utilized to adjust the position of the center of gravity of the head.
On the other hand, in the golfers, especially average golfers there are great demands for golf club heads with a low and deep center of gravity to produce a high launch angel with low spin for longer and straight drives.
In the U.S. Pat. No. 7,101,291, a wood-type hollow golf club head is disclosed, wherein a tubular socket is provided on the inside of the sole portion integrally with the sole plate, and a weight member is secured in the socket of the sole plate. In this structure, however, if the mass of the weight member is increased in order to lower and deepen the center of gravity of the head, as the tubular socket protrudes relatively high into the hollow of the head and the socket is filled with a heavy metal, a large stress acts on the root or lower part of the socket when striking a ball, especially when duffing a ball. Thus, the root part becomes a weak point, and in the worst case, the root part is cracked. As a result, the adjustable range of the position of the center of gravity is limited thereby.
A primary object of the present invention is therefore to provide a golf club head of which center of gravity is made lower and deeper by forming the sole portion with a sole plate having a large specific gravity.
A further object of the present invention is to provide a method for manufacturing a golf club head, by which the position of the center of gravity of the head can be adjusted in a wide range as desired and thus more lowing and deepening are possible without causing the weak point or damage.
According to one aspect of the present invention, a method for manufacturing a hollow golf club head comprises the steps of:
preparing a main frame made of a metal material and provided with a top opening and a bottom opening;
preparing a sole plate made of a metal material, wherein the metal material of the sole plate is larger in the specific gravity and smaller in the proof stress than the metal material of the main frame, and the sole plate comprises a main part which can almost fit to the bottom opening, and a protrusion which protrudes from the peripheral edge of an inner surface of the main part;
placing the sole plate in the bottom opening of the main frame so that the protrusion protrudes from the inner surface of an edge portion of the main frame around the bottom opening;
inserting a die into the inside of the main frame through the top opening;
caulking the sole plate by crushing the protrusion of the sole plate onto the edge portion around the bottom opening, by the use of the inserted die;
placing the crown plate in the top opening of the main frame; and
fixing the crown plate to the main frame.
Preferably, the main part of the sole plate is provided with a variable thickness gradually increasing from the front to the rear of the head.